Method and apparatus for supporting network slice when UE moves between 4G and 5G networks

ABSTRACT

The present disclosure relates to a communication method and system for converging a 5 th -Generation (5G) communication system for supporting higher data rates beyond a 4 th -Generation (4G) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. The present disclosure relates to a method of supporting a network slice of a network and a user equipment (UE) when the UE moves between a 4G network and a 5G network in the 3GPP 5G network technology.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority under 35 U.S.C. 119 toKorean Patent Application No. 10-2018-0094438 filed on Aug. 13, 2018 inthe Korean Intellectual Property Office, the disclosure of which isherein incorporated by reference in its entirety.

BACKGROUND 1. Field

The disclosure relates to a method of supporting a network slice of anetwork and a user equipment (UE) when the UE moves between a 4G networkand a 5G network in a wireless communication system, particularly, inthe 3GPP 5G network technology.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post LTE System’. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), Full Dimensional MIMO(FD-MIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud Radio Access Networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,Coordinated Multi-Points (CoMP), reception-end interference cancellationand the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) andsliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), and filter bank multi carrier (FBMC), non-orthogonalmultiple access(NOMA), and sparse code multiple access (SCMA) as anadvanced access technology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof Things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofEverything (IoE), which is a combination of the IoT technology and theBig Data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “Security technology” have been demanded forIoT implementation, a sensor network, a Machine-to-Machine (M2M)communication, Machine Type Communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing Information Technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies such asa sensor network, Machine Type Communication (MTC), andMachine-to-Machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RadioAccess Network (RAN) as the above-described Big Data processingtechnology may also be considered to be as an example of convergencebetween the 5G technology and the IoT technology.

There is a desire for a method of easily handing over a user session byapplying network slicing of a 5G network when a user equipment (UE)moves from a 4G network to the 5G network.

The above information is presented as background information only toassist with an understanding of the disclosure. No determination hasbeen made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

An aspect of the disclosure is to provide a method of handing over auser session by applying network slicing of a 5G network when a userequipment (UE) moves from a 4G network to the 5G network.

Also, another aspect of the disclosure is to provide a method of handingover a session, which performs communication with the same externalnetwork (data network (DN)) via multiple network slices in the 5Gnetwork, to the 4G network when a UE moves from the 5G network to the 4Gnetwork. According to an embodiment, a UE can continuously use a servicewhen the UE moves from the 4G network to the 5G network.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.

Moreover, various functions described below can be implemented orsupported by one or more computer programs, each of which is formed fromcomputer readable program code and embodied in a computer readablemedium. The terms “application” and “program” refer to one or morecomputer programs, software components, sets of instructions,procedures, functions, objects, classes, instances, related data, or aportion thereof adapted for implementation in a suitable computerreadable program code. The phrase “computer readable program code”includes any type of computer code, including source code, object code,and executable code. The phrase “computer readable medium” includes anytype of medium capable of being accessed by a computer, such as readonly memory (ROM), random access memory (RAM), a hard disk drive, acompact disc (CD), a digital video disc (DVD), or any other type ofmemory. A “non-transitory” computer readable medium excludes wired,wireless, optical, or other communication links that transporttransitory electrical or other signals. A non-transitory computerreadable medium includes media where data can be permanently stored andmedia where data can be stored and later overwritten, such as arewritable optical disc or an erasable memory device.

Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates an example structure of a network that supportsmobility between 4G and 5G networks;

FIG. 2 illustrates an example schematic operation according to anembodiment;

FIGS. 3A and 3B illustrate examples signaling procedure performed when aUE moves between 4G and 5G networks;

FIG. 4 illustrates example signaling procedure for session mapping whena UE moves between 4G and 5G networks;

FIG. 5 illustrates example configuration of an evolved nodeB (eNB)according to an embodiment;

FIG. 6 illustrates example configuration of an MME according to anembodiment;

FIG. 7 illustrates example configuration of an AMF according to anembodiment;

FIG. 8 illustrates example configuration of an SMF according to anembodiment; and

FIG. 9 illustrates example configuration of a user equipment (UE)according to an embodiment.

DETAILED DESCRIPTION

FIGS. 1 through 9 , discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged system or device.

Hereinafter, the operating principle of the disclosure will be describedin detail with reference to the accompanying drawings. In describing thedisclosure below, a detailed description of related known configurationsor functions incorporated herein will be omitted when it is determinedthat the detailed description thereof may unnecessarily obscure thesubject matter of the disclosure. The terms which will be describedbelow are terms defined in consideration of the functions in thedisclosure, and may be different according to users, intentions of theusers, or customs. Therefore, the definitions of the terms should bemade based on the contents throughout the specification.

Hereinafter, terms for identifying access nodes, terms indicatingnetwork entities, terms indicating messages, terms indicating interfacesbetween network entities, terms indicating various types ofidentification information, and the like are merely used for ease ofdescription. Therefore, the disclosure may not be limited by the termsprovided below, and other terms that indicate subjects having equivalenttechnical meanings may be used.

For ease of description, terms and names defined in the LTE and NRstandards, which are the latest standard defined by the 3^(rd)generation partnership project (3GPP) among the currently existingcommunication standards, will be used. However, the disclosure is notlimited by the terms and the names, and may be equally applied to asystem that complies with other standards. Particularly, the disclosuremay be applied to the 3GPP NR (the 5G mobile communication standard).

FIG. 1 illustrates example interworking structure between a 4G networkand a 5G network, which will be used for description of the disclosure.The interworking structure may include a mobility management entity(MME) 120 which is the control plane element of the 4G network, anaccess and mobility management function (AMF) 150 which is a controlplane element of the 5G network, and a session management function (SMF)170 and a user plane function (UPF) 160 which are common data planeelements of the 4G and 5G networks.

Referring to FIG. 1 , when a user equipment (UE) 100 moves from the 4Gnetwork to the 5G network, the MME 120 of the 4G network may transfercontext of the UE 100 to the AMF 150 of the 5G network via an interfaceN26 in a handover signal transmission process. The AMF 150 of the 5Gnetwork may enable the UE 100 to maintain the session that has been usedby the UE on the basis of the transferred context so that a service maybe provided to the UE without disconnection.

When the UE 100 accesses the 4G network, the UE 100 may camp on an LTEeNB (E-UTRAN) 110. The MME 120 may manage mobile context, sessioncontext, and security information associated with the UE 100. A servinggateway (SGW) 130 may provide a user plane function. The MME 120 and theSGW 130 may be in the same physical entity.

When the UE 100 accesses the 5G network, the UE 100 may camp on an NReNB 140. The 5G network may include an access and mobility managementfunction (AMF) entity 150. The AMF 150 may perform the same functions ofthose of the MME 120 of the 4G network, or may perform at least some ofthe functions. For example, the AMF 150 may manage informationassociated with access authorization of a core network of the UE 100 andinformation associated with mobility of the UE 100.

Also, for 4G-5G interworking, the communication system may include theUPF 160 (PGW-U+UPF or UPF+PGW-U), the SMF 170 (PGW-C+SMF or SMF+PGW-C),a policy control function PCF 180 (PCF+PCRF or PCRF+PCF) and a UDM 190(HSS+UDM or UDM+HSS).

For example, the UPF 160 may perform a routing function so that data istransmitted or received between the UE 100 and a data network on a userplane, and may perform an anchor function of allocating an Internetprotocol (IP) address corresponding to the data network.

The SMF 170 may allocate an IP address for the UE 100, may controlpolicy enforcement, and may perform general session managementfunctions.

The PCF 180 is in charge of policy rules. The UDM 190 may authenticatecredentials and assign access privileges.

FIG. 2 illustrates example network structure and operations performedbetween network elements, which will be used for description of thedisclosure. For ease of description, a description is provided withreference to signal messages explicitly shown in the drawing, andalthough a basic handover procedure is not described, the handoverprocedure is applied normally.

The schematic operation of the disclosure will be described withreference to FIG. 2 . First, in the process in which a UE 200 generateseach user session (PDN connection) for a data service in the 4G network,the UE performs a process of previously allocating a PDU session ID andsingle-network slice selection assistance information (S-NSSAI) of the5G network which correspond to the 4G PDN connection by utilizing aprotocol configuration option field of a session configuration signalmessage and an SMF 230. The S-NSSAI may be information for designating anetwork slice.

Second, if it is determined that the UE 200 needs to move from the 4Gnetwork to the 5G network on the basis of signal measurement informationof the UE 200, a 4G evolved nodeB (eNB) 210 may select a target eNB 270(in this instance, a 5G NG-RAN) to which the UE 200 is to move to. The4G eNB 210 may transfer a HO required message to an MME 220 in order tostart a handover procedure. The MME 220 may select the Iwk-AMF 240 thatsupports interworking between 4G and 5G on the basis of an AMF addressset by an operator. For example, not all AMFs and SMFs support a networkslice. In order to determine an AMF of a V-PLMN that supports a networkslice as a target AMF, the Iwk-AMF may be determined. The MME 220 maytransmit, to the Iwk-AMF 240, a handover request message includingcontext information of the UE stored in the MME 220. The Iwk-AMF 240identifies information associated with the SMF (H-SMF) 230 (multipleSMFs may be configured) corresponding to home-public land mobile network(H-PLMN) set for the UE 200 from the context information of the UE 200received from the MME220, in order to identify each PDU sessioninformation and mapped network slice information corresponding to eachPDN connection of the UE. In order to transfer session-relatedinformation of the user among the context of the UE to each SMF 230 ofthe H-PLMN, the IwK-AMF 240 may select at least one temporary SMF(V-SMF_TMP) (or a plurality of SMFs) corresponding to a visited PLMN(V-PLMN), and transmits the session-related information to the SMF(H-SMF) 230 of the H-PLMN via the SMF (V-SMF) of the V-PLMN.

Each SMF (H-SMF) 230 of the H-PLMN replies, to the Iwk-AMF 240, each PDUSession information and mapped network slice information correspondingto each PDN connection of the UE. The Iwk-AMF 240 may collect receivednetwork slice information and may select a target-AMF (T-AMF) 250capable of supporting all network slices (or network slices withpriority) configured for the UE. For example, the T-AMF 250 may supporthandover of the UE 200. The Iwk-AMF 240 may transmit, to the T-AMF 250,the handover request signal message received from the MME 220.

On the basis of the context information related to the session of theUE, each PDU Session ID, and network slice information, the T-AMF 250may select an SMF 260 of the V-PLMN for each PDU session. The SMF 260may be a V-SMF corresponding to a V-PLMN. The T-AMF 250 may transmit thecontext information of the UE to the V-SMF 260. According to the normalhandover procedure, the T-AMF 250 may transfer the handover requestmessage to the NR-RAN (5G eNB or 5G LTE eNB) 270 explicitly specified inthe handover request message, and the NG-RAN 270 may start withtransferring a handover response message to the T-AMF, and may completea handover standard procedure.

The NG-RAN 270 may store information associated with an identifier (UEID) of the UE 200 and information associated with the T-AMF 250.

Third, the UE 200 moves to the 5G network, sets up a radio connectionwith the 5G network, and transmits an RRC Configuration message to theNG-RAN 270 in order to complete handover. In this instance, the UE 200may include an MME ID in the message in the form of a mapped 5G-GUTI inorder to transfer MME information of the 4G network. The NG-RAN 270 maytransfer, to the T-AMF 250, the received mapped 5G-GUTI information inthe process of transmitting a path switch signal message to the T-AMF250 for completion of handover. The T-AMF 250 may determine that the UE200 moves from the 4G network on the basis of the received mapped5G-GUTI. The T-AMF 250 may transmit a handover complete signal messageto the Iwk-AMF 240 using Iwk-AMF ID information which is stored in thehandover preparation process in order to transfer a handover message.

The T-AMF 250 may transmit a PDU session update message to each SMF(V-SMF) 260 of the V-PLMN previously selected in the handoverpreparation process. Each SMF (V-SMF) 260 of the V-PLMN transmits anupdate message to an SMF (H-SMF) 230 of the H-PLMN corresponding to eachPDU session, so that the SMF (H-SMF) 230 of the H-PLMN does not transmita packet to the UE via the 4G network any longer, and transfers a packetto the UE via a data transmission path configured in the 5G network. TheIwk-AMF 240 (or a T-AMF autonomously performs identification if anIwk-AMF is not used) identifies the corresponding MME 220 of the 4Gnetwork on the basis of the mapped 5G-GUTI information included in thehandover complete message received from the T-AMF 250, and transfers thehandover complete message to the MME 220. The MME 220 may transfer aresponse message to the Iwk-AMF 240 in response to the handover completemessage. The Iwk-AMF 240 may transfer a handover complete responsemessage to the T-AMF 250.

FIGS. 3A and 3B illustrate examples signaling procedure for handoverthat maintains a user session and applies network slicing of the 5Gnetwork, when a UE moves from the 4G network to the 5G network. It ispreferable that FIGS. 3A and 3B are connected procedures.

According to the examples of FIGS. 3A and 3B, it is assumed that a UE300 accessed the 4G network, set up a plurality of PDN connections, andhas performed data transmission or reception when handover occurs. Also,it is assumed that the UE 300 and a network 340 (an SMF belonging to anH-PLMN (H-SMF)) transmits or receives a PDU session ID and network sliceinformation (S-NSSAI) to be used in the 5G network on the basis of acorresponding PDN connection, via a signal message in the process ofsetting up each PDN connection.

The process No. 1 of FIG. 3A is a process in which the UE detects the 5Gnetwork and measures the strength of a signal, and reports the same toan eNB in the 4G network.

The process No. 2 of FIG. 3A is a process in which the eNB selects atarget NG-RAN node of the 5G network and determines whether handover isneeded on the basis of the signal strength information received from theUE, and transfers a HO required signal message to an MME in order toinitiate a handover procedure.

The process No. 3 of FIG. 3A includes a process in which the MMEdetermines that handover is an inter-system handover which is performedbetween the 4G network and the 5G network on the basis of target NG-RANID information included in the HO required message received from theeNB, and a process of transmitting the HO required message using Iwk-AMFinformation, corresponding to the corresponding target NG-RAN ID and setin the MME.

The process No. 4 of FIG. 3A is a process of extracting an SMF ID of theH-PLMN (hereinafter, an H-SMF ID) from UE context information receivedfrom the MME, and selecting a temporary SMF in the V-PLMN (hereinafter,a V-SMF_TMP) which is capable of transferring a signal message to thecorresponding H-SMF in order to transfer the UE context information tothe H-SMF and obtain network slice mapping information.

The process No. 5 of FIG. 3A is a process in which the Iwk-AMF transmitsan SM context request signal message to the V-SMF_TMP selected in theprocess No. 4.

The process No. 6 of FIG. 3A is a process in which the V-SMF_TMPtransmits the SM context request signal message to the H-SMF.

The process No. 7 of FIG. 3A is a process in which the H-SMF transmits,to the V-SMF_TMP, an SM context response signal message including a PDUsession ID and network slice information (S-NSSAI) mapped for each PDNconnection (or EPS Bearer) of the 4G network.

The process No. 8 of FIG. 3A is a process in which the V-SMF_TMPtransmits, to the Iwk-AMF, the SM context response signal messagereceived from the H-SMF.

The process No. 9 of FIG. 3A is a process in which the Iwk-AMFdetermines a network slice list needed for providing the service for theUE on the basis of the PDU session information and the network sliceinformation (S-NSSAI) of the UE included in the SM context responsemessage, selects a suitable T-AMF that is capable of supporting allnetwork slices included in the list (or selectively supporting sliceswith priority), and transfers the HO required message received from theMME in the process No. 4 (in this instance, the IwK-AMF may make areference to a network slice selection function (NSSF), an NF repositoryfunction (NRF), or the like in order to select a T-AMF, depending onimplementation).

The process No. 10 of FIG. 3A is a process in which the T-AMF selects asuitable SMF in the V-PLMN (hereinafter, V-SMF) which is capable ofsupporting a network slice set in each PDU session for each PDU session,on the basis of the 4G UE context information and PDU session ID/S-NSSAIinformation included in the received HO required message, and transmitsa Create SM context request signal message.

The process No. 11 of FIG. 3A is a process in which a V-SMF selected foreach PDU session transfers the Create SM context request signal messageto the H-SMF.

The process No. 12 of FIG. 3A is a process in which the H-SMF allocatesa network resource required for a corresponding PDU session, andtransmits a create SM context response signal message including theresource allocation information to the V-SMF.

The process No. 13 of FIG. 3A is a process in which the V-SMF transmitsthe create SM context response message to the T-AMF.

The process No. 14 of FIG. 3A is a process in which the T-AMF transfersthe HO required message to the target NG-RAN node.

The processes Nos. 15 and 16 of FIG. 3A are processes of transferring aHO response message from the target NG-RAN node to the eNB of the 4Gnetwork.

Also, the process No. 17 of FIG. 3B performed after the processes ofFIG. 3A is a process in which the MME transmits a HO Command signalmessage that commands to perform handover to the 5G network, to the UEvia the eNB.

The process No. 18 of FIG. 3B is a process in which the UE transfers theID information of the MME that the UE has accessed in the 4G network, inthe form of a mapped 5G-GUIT via a signal message, in order to indicatehandover from the 4G network when the UE moves to the 5G network andsets up a radio link with the target NG-RAN node.

The process No. 19 of FIG. 3B is a process in which the NG-RAN nodecompletes setup of the radio link with the UE, and reports to the T-AMFthat the UE is successfully handed over.

The process No. 20 of FIG. 3B is a process in which the T-AMF determinesthat the UE is handed over from the 4G network on the basis of themapped 5G-GUTI information included in the signal message received fromthe NG-RAN node, and transfers a relocation complete notification signalmessage to the MME via the Iwk-AMF using the Iwk-AMF information storedin the process No. 5 (a temporary Iwk-AMF can be used in the case of astateless network, depending on implementation), in order to transfer,to the MME of the 4G network, the relocation complete notificationsignal message indicating successful handover.

The process No. 21 of FIG. 3B is a process in which the MME identifiesthe successful handover of the UE to the 5G network, cancels the storedUE context and network resources associated with the UE, and transfers arelocation complete notification ACK signal message to the T-AMF via theIwk-AMF.

The processes Nos. 22 to 25 of FIG. 3B are processes in which the T-AMFperforms transmission or reception of a signal message with each V-SMFand each H-SMF, in order to change a data transmission path associatedwith a corresponding PDU session of the UE from a 4G networktransmission path to a 5G network transmission path, for each PDUsession. Also, after the above-described processes are completed, the UEand the network may perform a mobility registration procedure defined inthe 5G standard, as needed.

Particularly, in operation S300 of FIG. 3A, the UE 300 may set up a PDNconnection in the 4G network. A PDU session ID and S-NSSAI may be givento the 4G network in each PDN connection setup process.

In operation S301, the UE 300 may transmit a measurement report to a 4GeNB 310. For example, the UE 300 explores a 5G network and measures asignal strength, and may report a result to the 4G network eNB 310.

In operation S302, the eNB 310 that receives the measurement report maytransmit a handover (HO) request message to an MME 330. In thisinstance, the eNB 310 may transmit a target 5G eNB ID (target NG-RAN ID)together. For example, the eNB 310 may determine a target 5G eNB on thebasis of the measurement report transmitted by the UE 300, and maytransmit the identifier of the determined target 5G eNB.

In operation S303, if it is determined that the MME 330 determines thatan inter-system handover between 4G and 5G networks is needed, anIwk-AMF 350 that supports interworking between the 4G and 5G networks isdetermined on the basis of the target 5G eNB ID.

In operation S304, the MME 330 may transmit a HO required message to thedetermined Iwk-AMF 350. In this instance, the MME 330 may transmit HOrequired message including UE context information of the UE 300.

The IwK-AMF 350 may extract an SMF ID (H-SMF ID) of a H-PLMN from the UEcontext information received from the MME 330. The Iwk-AMF 350 maytransfer the UE context information to the H-SMF 340. In order to obtainnetwork slice mapping information, the Iwk-AMF 350 may select atemporary SMF 370 in the V-PLMN (hereinafter, V-SMF_TMP) which iscapable of transferring a signal message to the H-SMF 340.

In operation S305, the Iwk-AMF 350 may transmit an SM context requestsignal message to the selected V-SMF_TMP 370. The SM context requestsignal message may be the context information of the UE, and may includeEPS bearer IDs (EBIs), which are bearer IDs used in the 4G network, andH-SMF IDs.

In operation S306, the V-SMF_TMP 370 may transmit the SM context requestsignal message to the H-SMF 340.

In operation S307, the H-SMF 340 may transmit, to the V-SMF_TMP 370, anSM context response signal message including a PDU session ID andnetwork slice information (S-NSSAI) mapped for each PDN connection (orEPS bearer) of the 4G network.

In operation S308, the V-SMF_TMP 370 may transmit, to the Iwk-AMF 350,the SM context response signal message received from the H-SMF 340.

In operation S309, the Iwk-AMF 350 may collect received network sliceinformation and may select the target AMF (T-AMF) 360 capable ofsupporting all network slices (or network slices with priority)configured for the UE. For example, the Iwk-AMF 350 may determine theT-AMF 360 on the basis of a PDU session ID and network slice information(S-NSSAI) mapped for each PDN connection (or EPS bearer) of the 4Gnetwork.

In operation S310, the Iwk-AMF 350 may transmit, to the T-AMF 360, thehandover request signal message received from the MME 330.

In operation S311, the T-AMF 360 may determine an SMF (V-SMF) 380 of theV-PLMN on the basis of the 4G UE context information and a PDU sessionID and network slice information (S-NSSAI) mapped for each PDNconnection (or EPS bearer) of the 4G network.

In operation S312, the T-AMF 360 may transfer the UE context informationto the V-SMF 380. For example, the V-AMF 360 may transmit theinformation via a create SM context request signal message.

In operation S313, the V-SMF 380 selected for each PDU session maytransmit a create SM context request signal message including UE contextinformation of the UE 300 to the H-SMF 340.

In operation S314, the H-SMF 340 may transmit an SM context responsemessage to the V-SMF 380. For example, the H-SMF 340 may allocate anetwork resource needed for a corresponding PDU session, and maytransmit a message including a PDU session ID and network sliceinformation (S-NSSAI) to the V-SMF 380.

In operation S315, the V-SMF 380 may transmit, to the T-AMF 360, the SMcontext response message including the PDU session ID and the networkslice information (S-NSSAI).

In operation S316, the T-AMF 360 may transmit a HO required message to atarget NG-RAN 320. In operation S317, the target NG-RAN 320 may transmita HO response message to the T-AMF 360.

In operation S318, the T-AMF 360 may transmit the received HO responsemessage to the eNB 310 via the Iwk-AMF 350 and the MME 330.

In operation S319 of FIG. 3B, the MME 330 may transmit a HO commandmessage to command the UE to perform handover to the 5G network, to theUE via the eNB 310. In this instance, the MME 330 may transmit the HOcommand including a target NG-RAN identifier.

In operation S320, the UE 300 may transmit the ID information of the MME330 that the UE 300 has accessed in the 4G network, in the form of amapped 5G-GUIT via a signal message, in order to indicate handover fromthe 4G network when the UE 300 moves to the 5G network and sets up aradio link with the target NG-RAN node. In this instance, the UE 300 maytransmit the mapped 5G-GUTI information and S-NSSAIs (H-S-NSSAIs)information of the H-PLMN via an RRC configuration message.

In operation S321, the target NG-RAN 320 may transmit a HO notifymessage after completing generation of the radio link with the UE, inorder to report, to the T-AMF 360, that the UE is successfully handedover.

In operation S322, the T-AMF 360 may determine that the UE 300 is handedover from the 4G network on the basis of the mapped 5G-GUTI informationincluded in the signal message received from the NG-RAN 320, and maydetermine that the successful handover is needed to be reported to theMME 330 of the 4G network.

Therefore, in operation S323, the T-AMF 360 may transmit a relocationcomplete notification signal message to the MME 330 via the Iwk-AMF 350.In operation S324, the MME 330 that receives the relocation completenotification signal message may transmit a relocation completenotification ACK message to the T-AMF 360 via the Iwk-AMF 350.

In operation S325, the T-AMF 360 may transmit a PDU session updaterequest message to the V-SMF 380. In this instance, in operation S326,the V-SMF 380 may transmit the received PDU session update message tothe H-SMF 340. In operation S327, the H-SMF 340 may transmit a PDUsession update response message to the V-SMF 380.

In operation S328, the V-SMF 380 may transmit the received PDU sessionupdate response message to the T-AMF 360.

In operation S329, the UE 300 may perform a mobility registrationprocedure with the 5G network.

FIG. 4 illustrates example signaling procedure for transmitting a 4G-5Gsession mapping policy between a UE and a network so that a user serviceis provided continuously when a UE moves between 4G network and 5Gnetwork.

In the state in which a UE in the 5G network communicates with the sameexternal data network (DN) using different network slices, if the UEmoves to the 4G network, since an external network having the same APNis incapable of communicating with the UE via different PGWs (in thecase of interworking, SMFs and UPFs), a single connection, via which aservice is continuously supported, needs to be selected amongconnections with the external data network via different network slices,which is a limitation. In order to overcome the drawback, there may beprovided a method of mapping to an APN of the 4G network inconsideration of each DNN (data network name) connected by each PDUsession generated in the 5G network and network slice information(S-NSSAI) which each PDU session belongs to.

According to the provided method, if different network slice information(S-NSSAI) is used for a PDU session having the same DNN, a different APNis mapped when a UE moves to the 4G network, and the above-describedlimitation does not matter. Also, when the UE moves to the 4G network,services may be provided continuously with respect to all PDU sessionsgenerated in the 5G network. The above-described mapping between a DNNand S-NSSAI and an APN may be performed autonomously by a UE and anetwork in a handover process by utilizing conversion policy informationset in advance between the UE and the network, instead of processing onthe basis of an explicit signal message in the handover process, inorder to minimize the effect of a change in implementation of the UE andthe network. The conversion policy information (set by an operator) formapping between the DNN and S-NSSAI and the APN may be set in the UE andthe network, before handover occurs, according to a registrationprocedure performed with the 5G network (or Attach or TAU procedureperformed with the 4G network) that the UE performs when the UEinitiates operation or moves, or a separate policy update procedure(steps 1 and 2). The conversion policy information may be included as itis, or as a part of path selection policy information of the UE, and maybe transmitted to the UE. Depending on an operator and implementation,the conversion policy information may be set in advance in the UE andthe network via a separate offline procedure.

Particularly, in operation S400, a UE 400 may determine to attach to the4G network. In operation S410, the UE 400 may transmit an attach requestto an MME 430 of the 4G network.

In operation S420, the MME 430 may identify a mapped policy which is setin advance or is received from a UDM, as described above. In operationS430, the MME 430 may transmit an attach accept message to the UE 400.In this instance, the MME 430 may transmit, to the UE 400, policyinformation for mapping between a DNN and S-NSSAI and an APN.

In operation S440, the UE 400 may determine to register with the 5Gnetwork. In this instance, the UE 400 may transmit a registrationrequest message to an AMF 440 in operation S450. In operation S460, theAMF 440 may identify the predetermined policy information for mapping.

In operation S470, the AMF 440 and a PCF 450 may search for and transmitor receive the policy information for mapping between the DNN andS-NSSAI and the APN.

In operation S480, the AMF 440 may transmit, to the UE 400, aregistration response message including the policy information formapping between a DNN and S-NSSAI and an APN.

FIG. 5 illustrates example configuration of an eNB according to anembodiment.

Referring to FIG. 5 , an eNB according to an embodiment may include atransceiver, a controller, and a storage unit. In the disclosure, thecontroller of the eNB may be defined as a circuit, anapplication-specific integrated circuit, or at least one processor.

The transceiver may perform transmission or reception of a signal withanother network entity. For example, the transceiver may receive a radiosignal from a UE, and may transmit a message for requesting handover toan MME.

The controller may control overall operation of the eNB according to thedisclosure. For example, the controller of the eNB may control a signalflow among blocks so that operations in the drawings and flowcharts areperformed.

The storage unit may store at least one piece of information transmittedor received via the transceiver, and information generated by thecontroller of the eNB. For example, the storage unit may storeidentification information (UE ID) of the UE of which a handoverpreparation process is completed, and mapping information of a T-AMF.

Particularly, the eNB may be a target eNB. In this instance, whenreceiving a handover request message from the T-AMF, the target eNB maystore information associated with the UE in the storage unit. When theUE transfers a control message (e.g., an RRC configuration message) tothe target eNB for network access during the handover process, thetarget eNB may control the transceiver to transmit an access requestmessage of the UE to the T-AMF stored for the UE.

FIG. 6 illustrates example configuration of an MME according to anembodiment.

Referring to FIG. 6 , an MME according to an embodiment may include atransceiver, a controller, and a storage unit. In the disclosure, thecontroller of the MME may be defined as a circuit, anapplication-specific integrated circuit, or at least one processor.

The transceiver may perform transmission or reception of a signal withanother network entity. For example, the transceiver may receive amessage for requesting handover from an eNB, or may transfer contextinformation of the UE to an AMF.

The controller may control overall operation of the MME according to thedisclosure. For example, the controller of the MME may control a signalflow among blocks so that operations in the drawings and flowcharts areperformed.

The storage unit may store at least one piece of information transmittedor received via the transceiver, and information generated by thecontroller of the MME.

FIG. 7 illustrates example configuration of an AMF according to anembodiment.

Referring to FIG. 7 , an AMF according to an embodiment may include atransceiver, a controller, and a storage unit. In the disclosure, thecontroller of the AMF may be defined as a circuit, anapplication-specific integrated circuit, or at least one processor.

The transceiver may perform transmission or reception of a signal withanother network entity. For example, the transceiver may receive contextinformation of a UE from the MME, and may transmit session-relatedinformation of the UE to an SMF.

The controller may control overall operation of the AMF according to theembodiment of the disclosure. For example, the controller of the AMF maycontrol a signal flow among blocks so that operations in the drawingsand flowcharts are performed.

The storage unit may store at least one piece of information transmittedor received via the transceiver, and information generated by thecontroller of the AMF. The AMF of FIG. 7 may be an Iwk-AMF that supportsinterworking, as described above. Alternatively, the AMF may be a targetAMF that supports handover of a UE and is determined by the Iwk-AMF.

If the AMF is an Iwk-AMF that supports interworking, the controller maycontrol the transceiver to receive protocol data unit (PDU) sessioninformation of a UE and network slice information from a sessionmanagement function (SMF) (H-SMF) corresponding to a home-public landmobile network (H-PLMN), and may determine a target AMF for supportinghandover of the UE on the basis of the received PDU session informationand network slice information.

Alternatively, the controller may control the transceiver to receive ahandover request message including UE context information from an MME.

The controller may select at least one temporary SMF (V-SMF)corresponding to a visited PLMN (V-PLMN), may control the transceiver totransmit session management information configured on the basis of theUE context information to the at least one selected temporary V-SMF, andmay control the transceiver to transmit the session managementinformation to the H-SMF via the at least one selected temporary V-SMF.

The determined target AMF may determine an SMF (V-SMF) corresponding tothe V-PLMN for each PDU session on the basis of the UE contextinformation, the PDU session information, and the network sliceinformation, and may transmit the UE context information to thedetermined V-SMF.

The controller may control the transceiver to transmit the receivedhandover request message to the determined target AMF.

The network slice information may be single-network slice selectionassistance information (S-NSSAI).

The IwK-AMF may be determined by a mobility management entity (MME) onthe basis of information associated with a 5G eNB for handover of the UEand the address of a predetermined AMF.

The case in which the AMF is a target AMF that supports handover of a UEwill be described. If the AMF is determined as a target AMF forsupporting handover of a UE by an interworking access and mobilityfunction (AMF) on the basis of the protocol data unit (PDU) session ofthe UE and network slice information, the controller may control thetransceiver to receive a handover request message including UE contextinformation, the PDU session information of the UE, and the networkslice information, and may determine a session management function (SMF)(V-SMF) corresponding to a visited PLMN (V-PLMN) for the PDU session ofthe UE.

FIG. 8 illustrates example configuration of an SMF according to anembodiment. The SMF may be an SMF corresponding to a H-PLMN or an SMFcorresponding to a V-PLMN.

Referring to FIG. 8 , an SMF according to an embodiment may include atransceiver, a controller, and a storage unit. In the disclosure, thecontroller of the SMF may be defined as a circuit, anapplication-specific integrated circuit, or at least one processor.

The transceiver may perform transmission or reception of a signal withanother network entity. For example, the transceiver may receivesession-related information of a UE from an AMF, and may transmit mappednetwork slice information according to an embodiment to the AMF.

The controller may control overall operation of the SMF according to theembodiment of the disclosure. For example, the controller of the SMF maycontrol a signal flow among the blocks so that operations in thedrawings and flowcharts are performed.

The storage unit may store at least one piece of information transmittedor received via the transceiver, and information generated by thecontroller of the SMF.

FIG. 9 illustrates example configuration of a UE according to anembodiment.

Referring to FIG. 9 , a UE according to an embodiment may include atransceiver, a controller, and a storage unit. In the disclosure, thecontroller of the UE may be defined as a circuit, anapplication-specific integrated circuit, or at least one processor.

The transceiver may perform transmission or reception of a radio signalwith an eNB according to an embodiment. For example, the transceiver maytransmit a measurement report to an eNB according to an embodiment, andmay receive an RRC configuration message corresponding to an HO commandfrom the eNB.

The controller may control overall operation of the UE according to theembodiments. For example, the controller of the UE may control a signalflow among the blocks so that operations in the drawings and flowchartsare performed.

The storage unit may store at least one piece of information transmittedor received via the transceiver, and information generated by thecontroller of the UE. According to the above-described method, if a UEperforms handover in the V-PLMN from the 4G network to the 5G network,although the UE transmits S-NSSAI corresponding to the H-PLMN to a 5GeNB, the 5G eNB may access an AMF suitable for the UE and may support anetwork slice since the 5G eNB stores the identifier of the UE andmapping information of a T-AMF that supports a network slice.

In the disclosure, a method in which an Iwk-AMF selects a T-AMF forsupporting a network slice for a UE is provided.

The method may include a process of transmitting or receiving a signalmessage in order to obtain network slicing information for the UE froman H-SMF, and the process includes a method of selecting a temporaryV-SMF-TMP. A method is provided in which the T-AMF sets a V-SMF on thebasis of the network slice information of the UE received from theIwk-AMF. A method is provided in which the T-AMF determines that the UEmoves from the 4G on the basis of information received from the UE, theT-AMF reports that handover is completed to the MME via the Iwk-AMF, inthe process in which the UE accesses the eNB via handover. In thisinstance, a method of storing an Iwk-AMF used in a handover preparationprocess and using the stored Iwk-AMF is provided.

Also, according to the disclosure, a method in which a UE maps networkslice information and an external network name connected to each 5Gsession of a UE to an external network name connected to a 4G sessionwhen the UE moves from the 5G network to the 4G network, may include amethod of mapping a pair of an external network name (5G DNN) connectedvia each 5G session and network slice information of the corresponding5G session to an external network name (4G APN) connected with a 4Gsession corresponding to the 5G session.

In the above-described detailed embodiments of the disclosure, acomponent included in the disclosure is expressed in the singular or theplural according to a presented detailed embodiment. However, thesingular or plural expressions are selected to be suitable for theprovided situations for convenience of description, and the disclosureis not limited to the singular or plural elements. An element expressedin a plural form may be configured in singular, or an element expressedin a singular form may be configured in plural.

Although the present disclosure has been described with variousembodiments, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method of a first access and mobilitymanagement function (AMF) for interworking between a 5G system (5GS) andan evolved packet system (EPS) in a wireless communication system, themethod comprising: receiving, from a mobility management entity (MME), ahandover request message including user equipment (UE) contextinformation; selecting a temporary session management function (SMF)corresponding to a visited-public land mobile network (V-PLMN)(V-SMF);transmitting, to a home-public land mobile network (H-PLMN) SMF (H-SMF)via the selected temporary V-SMF, session related information includedin the UE context information; receiving, from the H-SMF via theselected temporary V-SMF, protocol data unit (PDU) session informationand network slice information, the PDU session information beingassociated with session related information; and determining a targetAMF based on the network slice information; and transmitting, to thedetermined target AMF, the handover request message.
 2. The method ofclaim 1, wherein the UE context information includes SMF relatedinformation, and wherein the SMF related information is transmitted tothe selected temporary V-SMF.
 3. The method of claim 2, wherein theH-SMF is identified by the SMF related information.
 4. The method ofclaim 1, wherein the network slice information comprises at least onesingle-network slice selection assistance information (S-NSSAI).
 5. Themethod of claim 1, further comprising: receiving, from the MME,information associated with a 5G base station and an address of apredetermined AMF.
 6. A first access and mobility function (AMF) forinterworking between a 5G system (5GS) and an evolved packet system(EPS) in a wireless communication system, the first AMF comprising: atransceiver; and a controller coupled to the transceiver and configuredto: receive, from a mobility management (MME), a handover requestmessage including user equipment (UE) context information, select atemporary session management function (SMF) corresponding to a visited-public land mobile network (V-PLMN)(V-SMF), transmit, to a home-publicland mobile network (H-PLMN) SMF (H-SMF) via the selected temporaryV-SMF, session related information included in the UE contextinformation, receive, from the H-SMF via the selected temporary V-SMF,protocol data unit (PDU) session information and network sliceinformation, the PDU session information being associated with thesession related information, determine a target AMF based on the networkslice information, and transmit, to the determined target AMF, thehandover request message.
 7. The first AMF of claim 6, wherein the UEcontext information includes SMF related information, and wherein theSMF related information is transmitted to the selected temporary V-SMF.8. The first AMF of claim 7, wherein the H-SMF is identified by the SMFrelated information.
 9. The first AMF of claim 6, wherein the networkslice information comprises at least one single-network slice selectionassistance information (S-NSSAI).
 10. The first AMF of claim 6, whereinthe controller is further configured to: receive, from the MME,information associated with a 5G base station and an address of apredetermined AMF.